The present invention relates to thermal printers and more particularly to an improved thermal print head which maintains a uniform pressure against the print medium.
A printing wafer which contains a series of in-line dot thermal print elements as used in the present invention is described in U.S. Pat. Nos. 3,774,899 and 3,808,669. This wafer contains a plurality of elements each of which is heated when energized by an electrical signal. The heated element causes the formation of a dot upon a thermal sensitive paper which is in contact with the heating element. The intensity and clarity of the dot produced depends upon the proximity of the heating element to the paper and the tension exerted on the element against the thermal sensitive paper. The paper is supported by either a round or flat platen.
In previous high speed thermal printers the print element wafers are aligned on a printer frame in a given position in relation to the platen and are then rigidly fixed in place. This structure, however, is subject to a number of problems which can cause the intensity of the dot to vary and thereby adversely affect the clarity of the characters printed on the thermal sensitive paper. The letter quality will be degraded when either the proximity of the element to the paper or the tension of the element against the paper changes from some optimum setting. These conditions are present when the surface of the platen is irregular, the platen has a tapered shape or the sizes of the printer components vary due to thermal expansion or contraction.